Emerging lines of evidence suggest that interactions between genes and the environment play a critical role in individual vulnerability to psychiatric disorders including drug addiction. The epigenome is influenced by environment and thus is a highly relevant biological candidate to maintain persistent aberrant neuronal processing as a result of developmental drug exposure. The developing brain may be particularly sensitive to epigenetic influences, given the dynamic neuroplasticity characteristic of this period. Marijuana (Cannabis sativa) is the illicit drug most commonly used by pregnant women and teenagers. Our studies of human fetuses with maternal cannabis use revealed selective alterations of striatal preproenkephalin (PENK) and dopamine receptor D2 gene expression (predominantly enriched in striatopallidal neurons), but not prodynorphin or dopamine D1 receptors (enriched in striatonigral neurons). Similar gene expression patterns were detected in the ventral striatum of rats exposed to ?-tetrahydrocannabinol (THC), the psychoactive component of cannabis, prenatally as well as during adolescence. Importantly, PENK and D2 gene expression impairments persisted into adulthood following either prenatal or adolescent THC exposure and the animals exhibited increased heroin self-administration and inhibitory control deficit, phenotypes predictive of drug addiction vulnerability. Epigenetic modifications are capable of maintaining modified gene expression states that can persist throughout development and it is an intriguing possibility that such mechanisms would underlie the long-term effects of cannabis exposure. In this project, we propose to study chromatin modification at specific regulatory regions of the PENK and D2 genes in the ventral striatum of adult rats with developmental THC exposure. The fact that PENK and D2 genes are preferentially expressed in subpopulations of striatal neurons that constitutes the striatopallidal pathway suggests a potential THC-sensitivity of genes aligned to this circuit. We set out to discover novel striatopallidal genes that are affected by developmental THC exposure and explore the epigenetic mechanisms that regulate their expression. Furthermore, we will investigate the causal relationship between THC-sensitive striatopallidal genes and addiction-related behaviors by use of gene manipulation in the ventral striatum. Overall, these studies will provide important mechanistic insights into the long-term impact of developmental THC exposure that would enable the development of targeted treatment interventions for addiction vulnerability and other related psychiatric disorders associated with developmental insults.